Redundant array of independent disks is a disk group formed by combining a plurality of independent disks in different manners. From the user's perspective, a disk array RAID is like a disk but can provide higher storage capability than a single disk and it can also provide data backup. When data on a disk extent are damaged, the damaged data may be restored through data backup so as to protect the security of user data. The different combinations of disk arrays are referred to as RAID levels, such as RAID0, RAID1, RAID5 and so on.
With the development of disk array technology, the use of mapped disk array is increasing at present. Differing from the traditional disk array having disks that may be controlled separately, a plurality of mapped disk arrays may be mapped in one disk array so that a plurality of mapped disks arrays share one disk array, which greatly improves the utilization efficiency of the disk. However, when a disk array is used to store data, the stored data may sometimes overly concentrate on some disks, which makes these disks prone to failure, while replacing these faulty disks would lead to reduction of reliability and performance of the disk array.